feat(forms): Add untyped versions of the model classes for use in migration. (#45205)

We had previously introduced an `AnyForUntypedForms` type alias. However, given our updated migration plan, we actually want to use aliases for the model classes themselves. This commit introduces these aliases, and adds them to the public API. It must be merged before the types, in order to migrate google3.

PR Close #45205

goldens/public-api/forms/forms.md

@@ -143,9 +143,6 @@ export class AbstractFormGroupDirective extends ControlContainer implements OnIn
     static ɵfac: i0.ɵɵFactoryDeclaration<AbstractFormGroupDirective, never>;
 }
 
-// @public
-export type AnyForUntypedForms = any;
-
 // @public
 export interface AsyncValidator extends Validator {
     validate(control: AbstractControl): Promise<ValidationErrors | null> | Observable<ValidationErrors | null>;
@@ -725,6 +722,24 @@ export class SelectMultipleControlValueAccessor extends BuiltInControlValueAcces
     static ɵfac: i0.ɵɵFactoryDeclaration<SelectMultipleControlValueAccessor, never>;
 }
 
+// @public
+export type UntypedFormArray = FormArray;
+
+// @public (undocumented)
+export const UntypedFormArray: UntypedFormArrayCtor;
+
+// @public
+export type UntypedFormControl = FormControl;
+
+// @public (undocumented)
+export const UntypedFormControl: UntypedFormControlCtor;
+
+// @public
+export type UntypedFormGroup = FormGroup;
+
+// @public (undocumented)
+export const UntypedFormGroup: UntypedFormGroupCtor;
+
 // @public
 export type ValidationErrors = {
     [key: string]: any;